The halogenated hydrocarbons have been widely used as solvents and in other applications for many years. There have been developed numerous inhibitor systems to retard decomposition of certain of these halogenated hydrocarbons. In particular it has been found that such inhibitors are necessary to prevent decomposition and even detonation of certain halogenated derivatives of lower aliphatic hydrocarbons especially when these compounds are in contact with certain metals such as aluminum and iron. Without such an inhibitor a halogenated hydrocarbon can in a short time period decompose into a thick gummy carbonaceous mass quite unsuitable for most uses.
It has likewise been found that the halogenated hydrocarbon solvents should contain an additive to inhibit corrosion of metal objects brought into contact with such solvents. For example, U.S. Pat. No. 1,097,145 discloses the use of an unsaturated hydrocarbon additive to absorb chlorine radicals produced by decomposition of a chlorinated hydrocarbon by ultraviolet light, oxygen or other means thus preventing the chlorine radicals from attacking the metal.
A particular form of corrosion occurring in the storage and use of halogenated hydrocarbon solvents is crevice corrosion wherein small crevices of a metal in contact with the solvent become particularly susceptible to corrosion attack. The process is discussed in more detail in M. Henthorne, Fundamentals of Corrosion, Chem. Eng., 78(11), 127-132 (1971) wherein the following reasons for crevice corrosion occurring were formulated: (a) changes in acidity in the crevice, (b) lack of oxygen in the crevice, (c) buildup of detrimental ion species in the crevice, and (d) depletion of inhibitor in the crevice.
Particular compounds disclosed in the prior art as suitable inhibitors for use with halogenated hydrocarbon solvents to inhibit the decomposition of the solvent and to prevent crevice corrosion of metals include dioxane, nitromethane, cyclohexane, lower aliphatic alcohols and propylene oxide.
Dealloying, a particularly deleterious corrosion process, is the selective removal of one component of a metal alloy by a chemical medium. The process generally occurs over a relatively long time period and may often be unobservable since the physical dimensions and other qualities of the affected material may be unaltered, but the structure is changed and therefore the strength of the metal alloy is often severely decreased.
The dealloying or more specifically, denickelification of nickel-containing alloys exposed to aqueous systems has been previously reported, but to our knowledge this process has not been known to occur in an organic, non-polar, non-aqueous medium. It has now been found that when halogenated hydrocarbons are exposed to nickel alloys and especially alloys of copper and nickel, particularly at elevated temperatures and pressures over long time periods, a dangerous and heretofore unobserved condition may result from the denickelification of such alloys under the action of the halogenated hydrocarbon. That this newly discovered condition is not the result of known corrosion processes involving halogenated hydrocarbons is demonstrated by the fact that the previously mentioned known corrosion and decomposition inhibitors useful in halogenated hydrocarbon solvent systems are ineffective in protecting against this denickelification process.
Particular operating conditions wherein the above-described denickelification process may occur are in for example, heat recovery and transfer systems employing the aforementioned halogenated hydrocarbons in contact with nickel alloys at elevated temperatures and pressures. Included are such systems employing halogenated hydrocarbons as the working fluid whether cooling is occasioned through using the specific heat of the fluid to transport heat to a recovery or exchanger means or through using the latent heat of vaporization of the fluid, such as in systems where the vapor is condensed in a cooler or exchanger and the liquid recirculated to be revaporized.
It would therefore be desirable to provide an inhibitor for use with halogenated hydrocarbons, particularly halogenated hydrocarbons used in a heat recovery and transport system, that effectively prevents denickelification of nickel alloys when in contact with such halogenated hydrocarbons.